System Architecture Evolution (SAE) is the core network architecture of the 3rd Generation Partnership Project's (3GPP's) Long Term Evolution (LTE) wireless communication standard. Specifically, SAE is an evolution of a General Packet Radio Service (GPRS) core network, which reduces time delay and costs for operators, and provides a higher user data rate, higher system capacity, and better coverage.
FIG. 1 is a diagram illustrating a conventional SAE system.
Referring to FIG. 1, the conventional SAE system includes a User Equipment (UE) 101, i.e., a terminal device, for receiving data, an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) 102, a Mobility Management Entity (MME) 103, a Service GateWay (SGW) 104, a Packet data network GateWay (PGW) 105, a Policy and Charging Rule Function (PCRF) controller 106, a Serving GPRS Support Node (SGSN) 108, and a Home Subscriber Server (HSS) 109.
The E-UTRAN 102 is a wireless access network including a macro Evolved NodeB (eNB) that provides an interface for accessing the wireless network for the UE 101.
The MME 103 is responsible for managing mobile contexts, session contexts, and security information of the UE 101, and the SGW 104 is mainly used for providing functions of a user plane. Alternatively, the MME 103 and the SGW 104 may be embodied a single physical entity.
The PGW 105 is responsible for charging and legal monitoring, etc., and may also be embodied in a single physical entity with the SGW 104. The PCRF 106 provides Quality of Service (QoS) policies and charging criterions.
The SGSN 108 is a network node device for providing routing for the transmission of data in the Universal Mobile Telecommunications System (UMTS).
The HSS 109 is a home sub-system of the UE 101, for protecting user information, such as a current location, an address of a server node, user security information, and packet data context of the UE 101.
Along with enhancements of a service data rate of the UE 101, operators provide a new technology, i.e., Selected IP Traffic Offload (SIPTO). That is, when accessing a specific service, the UE 101 switches to an access point from the wireless access network, which is closer, in the movement procedure, to effectively reduce cost for the transmission network, and provide better service experiences for high data rate.
More specifically, 3GPP presents the network-supported SIPTO and the ability of Local Internet Protocol Access (LIPA). In the SIPTO, when the UE 101 accesses the Internet or other extra networks through a Home evolved NodeB (HeNB), Home NodeB (HNB), or a macro eNB, the network may select or re-select a user plane node which is closer to the wireless access network for the UE 101.
Although LIPA provides that when the UE 101 accesses a home network or an intra-company network through the HeNB or HNB, and the LIPA is executed, a user plane node close to the HNB or in the HeNB/HNB access network may be selected or re-selected for the UE 101. The user plane node may be a core network device or a gateway. The user plane node may be a SGW, PGW, or a Local GateWay (LGW) for the SAE system, and may be a SGSN or Gateway GPRS Support Node (GGSN) for the UMTS system.
FIG. 2 is a signal flow diagram illustrating a handover operation in a conventional SIPTO and LIPA.
Referring to FIG. 2, a source Base Station (BS) 251 decides to perform a handover of a UE 250 in step 201.
In step 202, the source BS sends a handover request to a source MME 253. The handover request includes information of a target BS 252, such as an IDentity (ID) of the target BS 252, or a target Tracking Area Identity (TAI), and further includes information such as a target Closed Subscriber Group (CSG) or handover type.
In step 203, the source MME 253 sends a forward handover request to a target MME 254. The forward handover request includes information of the target BS 252, etc., obtained from the handover request.
In step 204, if re-selecting an SGW for the UE 250, the target MME 254 performs a session establishing process with the re-selected target SGW 256. Accordingly, step 204 is not executed if the re-selection of the SGW for the UE 250 is not required.
In step 205, the target MME 254 sends a handover request to the target BS 252, and in step 206, the target BS 252 sends a handover request acknowledgement message to the target MME 254.
In step 207, the target MME 254 updates carrier information according to the target BS 252, with which the UE 250 switches, which specifically includes the target MME 254 requesting the establishment of a user plane tunnel between the target BS 252 and an LGW 257, to ensure the handover of UE 250 from the source BS 251 to the target BS 252.
Using the conventional handover procedure illustrated in FIG. 2, there are three common situations that result in handover failure and/or a waste of signaling/wireless resources.
Situation one: The target BS 252 and source BS 251 belong to different local HeNB networks. Thus, the target BS and source BS connect to different LGWs 257. As illustrated in FIG. 2, because the target BS 252 and source BS 251 connect to different LGWs 257, the handover fails. Further, although the target MME 254 may determine the handover failure when establishing the user plane tunnel, and thus, releases the established or occupied wireless resources, too many signaling resources and wireless resources have already been occupied, thereby wasting signaling and wireless resources.
Situation 2: The target BS 252 and source BS 251 belong to a same local HeNB network. However, the target BS 252 and source BS 251 connect to different LGWs 257, e.g., the target BS 252 and source BS 251 belong to different sub-networks, also resulting in the handover failure and the wasting of the signaling and wireless resources.
Situation 3: The target BS 252 and source BS 251 belong to a same local HeNB network, and the target BS 252 and source BS 251 may connect to a same LGW 257. However, the list of LGWs, with which the target BS 252 and source BS 251 connect is not the same, e.g., when the target BS 252 does not connect to the LGW 257 serving UE 250 at the source end, this also results in the handover failure and the wasting of the signaling and wireless resources.
Although, the problems in the conventional handover are described above with reference to an S1 handover procedure, if the source BS triggers an X2 handover process, the X2 handover process may fail, and the MME would not determine that the handover will not succeed until receiving a path switch request message, also wasting the signaling and wireless resources.
Furthermore, similar handover problems also exist in UMTS.
Basically, the above-described handover failure refers to the handover failure of the LIPA carrier. If a UE merely receives a LIPA service, the whole handover process performed according to the conventional handover will fail. However, if the UE simultaneously receives the LIPA service and non-LIPA service, the handover of the non-LIPA service performed according to the conventional handover flow may succeed, while the handover of the LIPA service will fail.